@article{SEDP_1973-1974____A4_0,
     author = {Helffer, B. and Zuily, C.},
     title = {Non hypoellipticit\'e des op\'erateurs diff\'erentiels du type de {Fuchs}},
     journal = {S\'eminaire \'Equations aux d\'eriv\'ees partielles (Polytechnique) dit aussi "S\'eminaire Goulaouic-Schwartz"},
     note = {talk:5},
     pages = {1--6},
     publisher = {Ecole Polytechnique, Centre de Math\'ematiques},
     year = {1973-1974},
     mrnumber = {404839},
     zbl = {0337.35018},
     language = {fr},
     url = {http://www.numdam.org/item/SEDP_1973-1974____A4_0/}
}